JP2010535442A - Communication unit and method for interference mitigation - Google Patents

Abstract

  The communication unit has a receiver for receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal. The receiver has a detection logic module configured to detect and process the composite communication signal as if at least one asynchronously received interference signal was received synchronously with the desired signal.

Description

  The field of the invention relates to wireless communication units that receive a desired signal when there is an asynchronously received interference signal. The field of the present invention is applicable to a UTRA (UMTS-Universal Mobile Telecommunication System-Terrestrial Radio Access) communication system, but is not limited thereto.

  The demand for high-bandwidth wireless communication does not wan, and the requirements imposed on cellular networks are constantly increasing. In particular, at the beginning of wireless multimedia communication, it is desirable to provide high data rate communication bi-directionally (ie, from and to a wireless subscriber communication unit) in a cellular communication system.

  However, since the radio spectrum is a valuable resource, it is common that the radio frequency used in one cell (service area) can be used simultaneously in neighboring cells (typically other overlapping service areas) as well. Is. Furthermore, resources used in one cell may be shared simultaneously among multiple users connected to that cell. Thus, in a cellular network, multiple simultaneous communications may occur at the same frequency or the same set of frequencies and at the same time.

  In such a communication network, a receiving communication unit (which may be a wireless subscriber communication unit or a base station) corresponds to a desired communication signal and also includes a plurality of potential simultaneous interference communication signals generated at the same frequency. A 'composite' signal representing is reached. The latter communication represents interference at the receiving communication unit. This effect needs to be mitigated in order to successfully demodulate the desired communication signal.

  Typically, the sustainable data rate on a communication link is called the desired signal reception level (SINR to Signal to Interference plus Noise Ratio) above some interference signal and noise level. Or in some cases simply reduced to SNR). Therefore, a high data rate can generally be achieved with a high SINR (or SNR) rather than a low SINR (or SNR).

  In a congested cellular environment with many wireless subscriber communication units that require simultaneous communication links, interference signals tend to dominate the background noise, so interference is an aspect that defines the achievable communication data rate. become. This is called an interference limited environment. Thus, it is clear that if the interference can be removed, a high SNR can potentially be realized with a corresponding increase in the communication data rate.

Typically, the interfering signal comes from three potential sources. That is,
(i) other simultaneous communication links within the same cell of the same communication system (this is commonly referred to as intra-cell interference)
(ii) Simultaneous communication links from other cells in the same communication system (this is commonly referred to as inter-cell interference)
(iii) Simultaneous communication links from other communication systems (such as leaks from communication systems operating in adjacent frequencies, other communication systems operating in the same frequency spectrum (ie, license-free spectrum), etc.)
Most advanced cellular communication systems are designed so that intra-cell interference is avoided or can be easily removed at the receiver. For example, in TD-CDMA, since intra-cell interference is detected, it is removed as part of the processing of the receiver using a multi-user detector (MUD). On the other hand, in OFDM, intra-cell interference is typically avoided by using orthogonal tones for different simultaneous users in the same cell.

  Interference from simultaneous communication links from other communication systems is somewhat difficult to remove. Basically, this can be performed as part of the processing of the receiver using further signal processing techniques.

  Inter-cell interference is difficult to avoid on a network scale in that it requires a scheduler that allocates orthogonal resources to simultaneous users through many cells in the network. Thus, one way to eliminate inter-cell interference is to allow the receiving communication units of the network to detect signals simultaneously from other cells in the communication network, not just from sources from the same cell. This can be described as an advanced or inter-cell capable multi-user detector (MUD). This description is in GB0412036.

  The aforementioned prior art refers to the case where all communication signals are synchronized or nearly synchronized (sometimes referred to as 'block' synchronization). For this patent specification, synchronization or block synchronization may be defined as including the case where another communication signal is received within a particular predetermined window. Typically, this predetermined window is a small percentage of timeslots, bursts, etc. For example, for TD-CDMA, this window is typically equal to the channel estimation window, and for OFDM, this window is typically equal to the cyclic prefix period.

  However, detection of inter-cell interference becomes quite complicated when the signal reaches the receiving device substantially asynchronously. This can occur because of the cells of the network that are asynchronous or because the distance between the cells is so large that the propagation times of the various communication propagation paths are substantially different.

  This latter case is illustrated in FIG. 1 for the downlink scenario. In FIG. 1, time-synchronized cellular base stations 105 and 110 transmit bursts 120 and 125, respectively. Bursts 120 and 125 are received by the wireless subscriber communication unit 115. Burst is a general term often used to include communication frames, slots, bursts, subframes, time slots, blocks of data, and the like. As shown, the receiving communication unit is located substantially closer to the transmitter 110 of cell A than the transmitter 105 of cell B. Thus, bursts 120, 125 are transmitted at the same time, but when received at the receiving communication unit 115, the bursts appear to be fairly 'asynchronous' as can be seen from the insertion timing diagram 135. Delay 130 is proportional to the difference in propagation path distance from each base station 105, 110 to receiving communication unit 115. This figure is for the downlink scenario (communication from the base station to the receiving subscriber communication unit), but it should be noted that the same applies to the uplink (communication from the transmitting subscriber communication unit to the base station). Should. That is, the base station and the subscriber communication unit may be exchanged in the drawing.

  In order to optimally detect asynchronous interference signals at the receiver, the configuration of the signals and / or communication signals processed within the receiver must be designed to handle the maximum expected delay 130 length. To emphasize this, reference is made to the TD-CDMA and OFDM examples described above.

  In TD-CDMA, the most common method of signal detection at a receiving apparatus is to use a linear MUD. Basically, such an algorithm performs a matrix operation on a vector of received signals and separates the signal into its constituent signal components. In the most common realization of linear MUDs, the main step is the inversion of the system matrix describing the configuration of the signals of the various simultaneous communication links and propagation channels that the signal undergoes. This can be extended to include inter-cell communication signals as described in GB412036. In such a method, the complexity of the detection operation is directly related to the duration of the propagation channel assumed in the system matrix, and a long period of propagation channel introduces considerable additional complexity in the detection operation.

  Thus, optimal detection of inter-cell TD-CDMA signals is sufficient for the MUD channel window to contain the desired signal components and the expected asynchrony of the inter-cell communication signal as shown in FIG. I need that. If the cellular communication system is asynchronous, or if the communication signal is assumed to traverse a long distance, this channel window will quickly become unacceptably large, especially a detection algorithm that is not feasible at the receiving communication unit. Bring.

  Therefore, in practice, the MUD is designed with an acceptable channel window from an implementation point of view, and the level of asynchrony allowed in the receiver architecture to make it possible to detect signals that arrive within the channel window. Dominated by the channel window. Thus, signals with delays greater than the implemented channel window remain undetected.

  For 3GPP high chip rate TD-CDMA, the burst configuration is typically designed to allow a channel window of 57-64 chips, which represents a small percentage of the total burst period of 2560 chips . Typically, the MUD for this application is designed to accommodate this channel window period. Thus, it is clear that such systems can only tolerate a limited amount of asynchrony before inter-cell communication signals become undetectable, and therefore before inter-cell interference stops mitigating. .

  An OFDM system typically uses bursts or symbols having a data portion and a cyclic prefix or suffix. For simplicity, the implementation described below refers only to the cyclic prefix case. However, those skilled in the art will appreciate that the concepts of the present invention can be applied to cyclic prefixes or cyclic suffixes. The cyclic prefix is the same as the channel window in TD-CDMA described above. That is, the cyclic prefix is provided to allow any multipath delay experienced by the communication signal when passing through the propagation environment.

  A cyclic prefix is formed by copying the last few samples of the data portion of the burst and adding them to the beginning of the data portion, thus creating a periodically symmetric burst or symbol. In an OFDM receiver, the data portion is extracted from the cyclic prefix and converted to the frequency domain where the individual tones are orthogonal. If a tone constitutes a communication signal from multiple cells, these can be optimally separated.

  However, if the data extraction of the OFDM burst is not precisely adjusted and begins earlier than the beginning of the cyclic prefix or later than the end of the cyclic suffix, the extracted portion is no longer cyclically symmetric. Thus, when converted to the frequency domain, the individual tones are not orthogonal and optimal detection of various communication signals is no longer a feasible operation.

  Therefore, as with TD-CDMA, a limited amount of inter-cell communication signals cannot be detected by OFDM implementation, and therefore before inter-cell interference stops being mitigated by normal means. It is clear that only asynchrony is acceptable.

  The above example serves to illustrate the disadvantages of the prior art when the interfering signal is substantially asynchronous. This state represents an asynchronous cellular communication system, or one that has a significant distance between cells, or in fact that other communication links are not necessarily part of the cellular communication system.

  Thus, an improved wireless communication unit having a multi-signal detector is advantageous, particularly a multi-signal detector that allows increased flexibility, improved performance, improved detection and / or increased interference suppression. is there.

  Accordingly, the present invention is directed to alleviating, mitigating or eliminating one or more of the above-mentioned drawbacks singly or in any combination.

  According to a first aspect of the present invention, a communication unit is provided. The communication unit has a receiver for receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal. The receiver has a detection logic module configured to detect and process the composite communication signal as if at least one asynchronously received interference signal was received synchronously with the desired signal.

  The present invention may allow improved use of communication resources in a communication system, for example by providing an accurate estimate of the received signal in a communication system in which there is an interfering (and substantially asynchronous) signal.

  The present invention may allow a communication link to operate when there is a significant level of interference (eg, from other simultaneous links). In this case, it is considered that two (or more) communication links are time asynchronous.

  The present invention may allow improved performance perceived by end users, for example by allowing a communication link to operate at a high signal to noise ratio (SNR). Thus, a corresponding increase in data throughput can be provided.

  According to an optional feature of the invention, the communication unit may further comprise a synchronous logic module operably coupled to the detection logic module, wherein the composite communication signal is at least one asynchronous with the desired signal. Are input to a synchronization logic module that synchronizes the timing of the communication unit with both the received interference signal.

  According to an optional feature of the invention, the communication unit may further comprise a channel estimation logic module operatively coupled to the detection logic module, wherein the desired signal and at least one asynchronously received interference The signal is applied independently to each channel estimation logic module.

  According to an optional feature of the invention, the detection logic module may discard at least one asynchronously received interference signal following execution of the detection operation.

  According to an optional feature of the invention, the detection logic module calculates at least one of the timing of at least one asynchronously received interference signal and the phase shift of at least one asynchronously received interference signal. It may be configured to be ignored. In this manner, the detection logic module may process at least one asynchronously received interference signal within the processing window of the desired signal received in response to the ignore operation.

  According to an optional feature of the invention, the detection logic module may comprise at least one of a joint detector, a linear detector, a multi-signal detector, and a multi-user detector.

  According to an optional feature of the invention, the composite communication signal may comprise at least one burst of time slot communication signals, and in certain embodiments, the time slot signals are time division code division multiplexed (TD). -CDMA: time-division code division multiple (OFDM) access communication signal or orthogonal frequency division multiplexed (OFDM) communication signal.

  According to an optional feature of the invention, the communication unit may be a radio base station or a radio subscriber communication unit.

  According to an optional feature of the invention, the communication unit may be configured to support 3GPP (3rd Generation Partnership Project) cellular communication. Thus, the present invention may be compatible with any existing communication system such as a 3GPP TD-CDMA or TD-SCDMA cellular communication system.

  According to a second aspect of the invention, a method for interference mitigation in a communication system is provided. The method includes receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal. The method further comprises detecting and processing the composite communication signal as if at least one asynchronously received interference signal was received synchronously with the desired signal.

  According to a third aspect of the present invention, an integrated circuit is provided. The integrated circuit includes a logic module that receives a composite communication signal having a desired signal and at least one asynchronously received interference signal. The integrated circuit further includes a detection logic module configured to detect and process the composite communication signal as if at least one asynchronously received interference signal was received in synchronization with the desired signal.

  According to a fourth aspect of the present invention, a computer program product is provided. The computer program product has program code for mitigating interference in a cellular communication system. The computer program product receives a composite communication signal having a desired signal and at least one asynchronously received interference signal, and whether the at least one asynchronously received interference signal is received synchronously with the desired signal. As such, it has program code for detecting and processing composite communication signals.

  According to a fifth aspect of the present invention, a communication system is provided. The communication system includes a communication unit capable of receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal. The receiver includes a detection logic module that detects and processes the composite communication signal as if at least one asynchronously received interference signal was received synchronously with the desired signal.

  The above and other aspects, features and advantages of the present invention will become apparent from and will be elucidated with reference to the embodiments described hereinafter.

Known simplified conceptual diagram with emphasis on propagation distance of synchronous downlink cellular communication system Communication unit receiver adapted according to an embodiment of the invention A series of inter-cell waveforms for channel estimation of interfering signals and desired signals to clarify the use of channel windows in a cellular system according to an embodiment of the present invention. A series of inter-cell waveforms including channel estimation of the own cell and time-shifted channel estimation of the interference signal according to an embodiment of the invention Flowchart of signal acquisition, tracking and channel estimation mechanism according to an embodiment of the present invention. Exemplary computing system that can be used to implement the processing functions of embodiments of the present invention

  Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

  In summary, embodiments of the present invention describe a sub-optimal detection method at a receiving communication unit that mitigates one or more of the aforementioned problems associated with receiving a substantially asynchronous communication signal. The proposed wireless communication unit and detection method allows simultaneous detection of substantially asynchronous communication signals and thus can provide interference mitigation functions in such an environment. This allows the communication link to operate with a high signal-to-noise ratio (SNR) and can therefore provide a corresponding increase in data throughput.

  As will be appreciated by those skilled in the art from a brief description of the problem provided in the preceding paragraph, optimal detection of substantially asynchronous interference signals at the receiving device is a fairly complex operation. However, by applying some sub-optimal approximations to the reception problem, substantially asynchronous interference signals can be detected at the receiving device, thus reducing the interference. Embodiments of the present invention transmit signals in burst and / or time slot format (eg, data units or chunks are grouped together and transmitted over the air interface in block, burst or time slot format, etc.). In particular to communication systems.

  The inventive concept will be described with respect to an embodiment of time division code division multiple access (TD-CDMA) consistent with the block, burst or time slot radio interface format described above. However, it can be appreciated that the concepts of the present invention can be readily applied to other block, burst or time slot radio interface formats, such as implementations of orthogonal frequency division multiplexing (OFDM) radio interfaces.

  In an implementation of TD-CDMA, it may be possible to remove explicit synchronization procedures used for asynchronous interference signals.

  The foregoing embodiments of the invention refer to a linear detector (eg, a detector in the form of a de-correlator or a minimum mean square error (MMSE) linear detector). However, it is within the scope of the present invention that other detection techniques may be used and the inventive concept is not limited to linear detectors.

  According to embodiments of the present invention, the inventive concept is described below with respect to a multi-signal detector. A multi-signal detector may be referred to as a multi-user detector, a joint detector, a multi-chip equalizer, etc., as is known to those skilled in the art.

  It is envisaged that the inventive concept described below may be used in the uplink or downlink transmission direction. Thus, regardless of whether Node B (or a base station) is using a receiver or a user equipment (or other wireless subscriber communication unit) is using a receiver, embodiments of the present invention The signal detection operation will be described.

  Further, it is envisioned that the concepts of the present invention are not limited to cellular communication systems, but are applicable to any wireless communication system or wireless communication unit that uses burst or time slot receivers.

  In summary, embodiments of the present invention describe and focus on detection methods applicable to UTRAN (Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network) specifications. Such UTRAN system and its operation are described in detail in 3GPP (3rd Generation Partnership Project) technical specification documents 3GPP TS 25.401, 3GPP TS 23.060 and related documents available from 3GPP website (www.3gpp.org) Therefore, it will not be described in detail here.

  Referring to FIG. 2, a block diagram of a received signal processing logic module 200 of a wireless communication unit adapted according to an embodiment of the present invention is shown. As will be appreciated by those skilled in the art, block diagrams of the described embodiments of the present invention (eg, a block diagram of received signal processing logic module 200) may apply equally to both a wireless subscriber communication unit and a base station unit. is assumed.

  Receive signal processing logic module 200 includes a plurality of radio frequency (RF) receiver circuits grouped and shown as receive block 210 that receives composite RF input signal 205. The RF receive block 210 includes, for example, RF amplification, RF downmixing, appropriate filtering to remove unwanted adjacent channel signals, and an analog-to-digital converter that converts the received analog signal to a digital equivalent. You may have.

  The digital output of the RF receive block 210 is provided to a synchronization logic module 215 configured to synchronize the receiver to the desired signal. In certain embodiments of the present invention, the digital output of the RF receive block 210 is also provided (in parallel) to a further synchronization logic module 225 configured to synchronize the receiver to one or more received interference signals. May be. The output of the synchronization logic module 215 is input to the channel estimation logic module 220 to perform channel estimation of the desired signal as shown in FIG. Similarly, in certain embodiments of the present invention, the output of synchronization logic module 225 may also be input to channel estimation logic module 230 to perform channel estimation of one or more interference signals.

  In one embodiment of the invention, the output of the desired channel estimation logic module 220 is input to the detector 235 along with the output of the interference channel estimation logic module 230. The detector 235 may be a multi-signal detector, a multi-user detector or a joint detector. In an embodiment of the invention, detector 235 decodes the desired signal and one or more interfering signals together, as described below with reference to FIGS. Accordingly, the detector 235 extracts the desired symbol 245 and discards the interference signal symbol 240 in some embodiments of the invention.

  Once the correct desired signal symbol is extracted, it is input to the symbol demodulation logic module 250 to demodulate the received signal.

  The output of demodulator 250 may provide a demodulated signal to further signal processing logic module 255. Further signal processing logic module 255 may include bit level processing, deinterleaving, error correction, decoding, and the like.

  The adaptation of the detector 235 will be described in the TD-CDMA embodiment of the present invention.

  In cellular communication systems that use TD-CDMA radio interface technology, a receiver called a multi-user detector (MUD) is commonly used to detect the received signal at the receiver and reduce the effects of inter-cell interference. It is common to use. Assuming that some knowledge of the interference signal is available and the interference is almost synchronous or block synchronized, the operation of the MUD is to detect spreading codes from other cells to identify inter-cell interference. It may be expanded to include. Examples of this technique can be found in the literature “Co-channel Interference Mitigation Detectors for Multirate Transmission in TD-CDMA Systems”, IEEE JSACm Vol. 20, No. 2, Feb. 2002 by Piero Castoldi and Hisashi Kobayashi.

  According to an embodiment of the present invention, joint detection of both a desired signal and an interference signal is performed in the case of TD-CDMA. For TD-CDMA implementations, the timing Δ (timing difference) is determined between the absolute timings of the received desired signal and one or more received interference signals in the received decoded signal. As is known, the absolute timing of the desired signal may be obtained using any known synchronization or tracking procedure. It is envisioned that the absolute timing of one or more interfering signals may be obtained using another synchronization / tracking procedure or may be obtained using a channel estimation procedure using a large search window. .

  Thereafter, according to an embodiment of the present invention, the determined absolute timing of the interference signal is adjusted so that its channel estimate falls within the detection window of the desired signal. The complexity of the joint detection operation at detector 235 is related to the size of the detection window. Thus, advantageously, the time shift of the absolute timing of the interference signal in the TD-CDMA implementation results in a joint detection operation that can receive and process the desired signal and the interference signal received asynchronously, Assume that the signals are received synchronously so that both channel estimates are within the same normal size window. In this way, the channel estimation logic module performs channel estimation of both the desired component and the interference component of the decoded signal separately. Thus, advantageously, joint detection that is not prohibitively complex can be performed.

  In order to accurately perform the detection process at the detector 235, timing information of both the desired signal and the interference signal should be considered. Nevertheless, as an attempt to provide another point of view of the concept of the present invention described above, a concept is considered in which the absolute timing information of the interference signal is discarded and only the channel estimation of the joint detection process is used. In particular, joint detection processing that takes into account the timing information of both the desired signal and the interference signal is prohibitively complicated when the signals are quite asynchronous.

  Thus, according to an embodiment of the present invention, as long as the detector uses all the extracted information about the desired signal and only uses some of the information about one or more interfering signals, the system model A suboptimal approximation of may be used. The inventors of the present invention have identified that this typically provides better performance than the usual approach of ignoring asynchronous interference all at once.

  It is envisioned that the time shifting operation (or removal of the absolute timing of the interfering signal) may result in some corruption of the detected interfering signal, but this detected interfering signal is discarded and is therefore irrelevant. An important aspect from a performance point of view is that it is assumed that there is an interfering signal when joint detection is performed, so using any collected information about the interfering signal is Since it is more desirable not to have this information, better performance can be obtained.

  According to an embodiment of the present invention, the joint detection process includes detector 235 generating a system matrix (eg, a matrix describing the transmission of various signals). The columns of the system matrix are formed by convolving the effective spreading code of the signal detected in the estimation of the propagation channel from the transmitter to the receiver as implemented in the channel estimation logic module 220, 200 of FIG. .

  For TD-CDMA, joint detection logic module 235 performs inversion of the system matrix (or other matrix based on the system matrix in some embodiments) for each type. For example, in this case, inversion is performed explicitly. This is especially true for the previously described linear detection techniques such as linear minimum mean squared error (LMMSE) or zero-forcing (ZF). That is, in linear techniques, a model of the system (ie, a system matrix) is built and inverted to obtain the desired result.

  The system matrix (ie, the matrix describing the transmission of various signals) is composed of vectors formed by convolving the signal's effective spreading code with an estimate of the propagation channel from the transmitter to the receiver. Each channel estimation performed in the detection process is described mathematically as follows.

ただし、

However,

は、検出される第kの信号の有効な拡散コードであり、

Is a valid spreading code of the detected k th signal,

は、受信機への送信で第kの信号が受ける推定離散時間伝搬チャネルを表し、
*は、畳み込み演算を表す。

Represents the estimated discrete time propagation channel that the kth signal will receive in transmission to the receiver,
* Represents a convolution operation.

  A valid spreading code may have a spreading code and a cell-specific scramble code in the case of the UMTS 3GPP high chip rate standard, typically a short period (eg 16 chips in this example) (3GPP The specifications of the physical layer are described in TS25.211, and the portions describing the implementation of the scramble code and spreading code are in TS25.211 and TS25.223). The estimated channel impulse response is designed to account for expected multipath propagation delays in a cellular environment. In the aforementioned standards, this is typically a period of 57 or 64 chips, depending on the burst configuration in operation. Therefore, the maximum length of the system matrix vector is typically 79 chips or less.

  The system matrix vectors for all detected K signals are concatenated to form a system submatrix B as shown in equation [2]. The plurality of system sub-matrices are concatenated with a zero-padding offset to form a system matrix A as shown in Equation [3]. The length of the zero padding offset applied to each submatrix of the configuration of A as described above is a multiple of the effective spreading code length (ie, 16 chips in this example). Therefore, the system matrix A is a block-banded diagonal matrix.

受信ダイバーシチが使用される場合、複数のシステム行列は、各受信アンテナのチャネル推定から形成され、これらは、全体システム行列を得るために垂直に重ねられる。しかし、明瞭にするために、提示される式ではこれは省略される。

When receive diversity is used, multiple system matrices are formed from the channel estimates for each receive antenna, and these are superimposed vertically to obtain the overall system matrix. However, for the sake of clarity this is omitted in the formulas presented.

  The linear MUD technique generally used in the TD-CDMA system requires inversion of the system matrix described in [3] or inversion of a matrix constructed from the system matrix. The complexity of this inversion depends on the diagonal depth of the block band of the matrix. As the number of rows in the block band increases, or similarly, the number of rows in the system submatrix B increases, the inversion complexity increases dramatically.

  In a scenario where asynchronous inter-cell interference exists, the channel estimates for the separate signals are typically (although not necessarily) shown in FIG. 5 via correlation between a set of known channel estimation sequences and the received signal. Obtained independently as shown.

  Referring now to FIG. 3, a series of inter-cell channel estimates of both the interference signal and the desired signal are shown to clarify the use of the channel window in a wireless communication unit according to an embodiment of the invention. Has been. The channel estimates for the desired cell signal 310 and interference signal 320 are separated by a delay 315 as shown. This delay 315 is due to the difference in arrival time between the desired burst and the interference burst.

  In order to properly consider this delay 315 in the system matrix, the system matrix column of equation [1] needs to be reasonably long. For example, the channel estimate for the desired cell is typically within the channel window 305 having the aforementioned '57' or '64' chips. However, the interference channel estimate has a delay 315 that can be several times this delay (up to 20 times) before the channel estimation begins. This means that the estimated channel impulse response of the interference signal has a zero at the start corresponding to the period of delay. This leads to a system submatrix with substantially many rows (up to 20 times in the previous example). Therefore, the inversion complexity of the system matrix becomes prohibitive.

  Referring now to FIG. 4, a series of inter-cell waveforms 400 are shown that include a desired cell channel estimate 415 and a time-shifted interference signal channel estimate 420 in accordance with an embodiment of the present invention. Thus, according to one embodiment of the present invention, the channel estimation of the interference signal is deliberately shifted in time to occur within the allowed channel window 405 as shown in FIG. Since the system submatrix is constructed within the channel estimation period (eg, 57 or 64 chips), the inversion of the system matrix is as complex as the currently known nearly synchronous case.

At the output of the linear detector, the symbols are demultiplexed into those from the desired signal and those from the asynchronous interference signal. Due to the nature of the time shift performed in the interference channel estimation, the output symbols detected from the asynchronous interference signal may be delayed, may be corrupted due to delay, and thus may be discarded. This approximation does not make assumptions about the constellation of the output symbols for a particular type of detector, so only output symbols associated with non-time-shifted channel estimates (desired signals) will be output constellation. Due to the fact that it necessarily appears in the correct location, it is assumed that in an alternative embodiment of the invention, the inventive concept may be applied to a cellular communication system using OFDM radio interface technology. . In this case, inter-cell interference is generally avoided by using orthogonal tones for different simultaneous users within the same cell. Typically, synchronization is obtained by correlating the received signal in the time domain with a known synchronization sequence. In known OFDM systems, known frequency domain pilots are extracted from orthogonal tones and used to provide a basis for frequency domain channel estimation of the signal of the own cell. This channel estimate may be used to phase and amplitude equalize each orthogonal tone and allow accurate demodulation for the transmitted modulation symbols.

  In the case of co-received interfering OFDM bursts, the channel estimates from both bursts may be used to further separate the individual orthogonal tones into the component desired and interfering signals. However, when extraction of the data payload of the desired burst is performed as described above, if there is an interference burst or OFDM symbol that is substantially asynchronous with that of the desired signal, extraction of the interference burst or OFDM symbol The done part is not necessarily cyclically symmetric. Thus, when demodulated in the frequency domain, the interference tones are no longer orthogonal. This can have the result that the known pilots of the interference burst or OFDM signal can be corrupted and therefore accurate channel estimation of the interference signal can be difficult or impossible. This results in the detected tones being potentially inseparable into the component desired and interfering signals.

  The concept of the present invention described above obtains an uncorrupted channel estimate of the component signal by channel estimation of the desired signal component and the interference signal component separately (discarding absolute time information). It can also be applied to OFDM implementations by utilizing some information of the interfering signal and thus approximately separating the received signal into the desired and interfering components of its components. Therefore, the joint detection logic module in the OFDM embodiment of the present invention can handle not only signals that are assumed to be synchronized, but also interference signals that are substantially asynchronous, so that known OFDM joint detection logic modules and Is different.

  Referring now to FIG. 5, a flowchart 500 illustrates a signal acquisition, signal tracking and channel estimation mechanism according to an embodiment of the present invention. First, the flowchart 500 begins with the communication unit detector processing the received signal and then determining signal acquisition and signal tracking of the desired signal, as shown in step 510. Signal acquisition and tracking of the desired signal is performed according to known techniques related to the radio interface technology used in the communication system.

  Next, as shown in step 515, the detection logic module of the communication unit performs channel estimation of these desired signals. Channel estimation is performed to determine an estimate of the propagation channel experienced by the desired signal in transmission from the transmitter to the receiver.

  Further, as shown in step 520, the detection logic module of the communication unit may extract information necessary to detect a desired signal. Such further information may be extracted from a channel estimation process that aids detection, such as information about spreading codes present in CDMA systems or modulation schemes in operation of OFDM systems.

  At the same time, according to an embodiment of the present invention, as shown in step 530, the detection logic module of the communication unit processes the received signal and then determines signal acquisition and signal tracking of the interference signal. Next, as shown in step 535, the communication logic of the communication unit performs channel estimation of these interference signals. As shown in step 540, the detection logic module of the communication unit may extract any information about the nature of the interference signal. Due to the undue requirement of alternative communication systems that inform all receiving communication units of all potentially simultaneous communication signals, typically this information is less than the amount of information available for the desired signal. is there.

  In certain embodiments of the invention, it is envisioned that the next step (not shown) may define a time delay between the desired signal and the interference signal. This may be determined using the acquisition, tracking or channel estimation information determined in the previous step.

  Here, as shown in step 545, the detection logic module of the communication unit shifts the channel estimation of the interference signal in time so that the processed interference signal is located within the desired signal detection window. In some embodiments of the present invention, the channel estimation of the interference signal may be effectively time shifted by an amount that puts the interference signal within the channel window of the detector. The time shift of channel estimation does not correspond to the physical shift of some entity, but corresponds to the interpretation that the interference signal is within the input composite signal (desired signal + some interference and noise). The channel window may be a detection window of a communication system based on a time domain (for example, TD-CDMA or the like), or may be a cyclic prefix of a communication system based on a frequency domain (for example, OFDM).

  In this way, the detection logic module determines the presence and identification of any interfering signals in the received signal.

  In some embodiments of the invention, the processing of the interference signal by the detection logic module may be performed in series with the processing of the desired signal as compared to the simultaneous processing of the interference signal and the desired signal.

  Thereafter, as shown in step 550, the detection logic module of the communication unit uses the information extracted from the desired channel estimate in step 520 and the time-shifted interference signal estimate from step 540 to receive the received signal. Perform joint detection with. Appropriate suboptimal joint detection techniques may be performed by assuming that the previous asynchronous signal is actually a synchronous or nearly synchronous signal (eg, a block synchronous signal).

  As shown in step 555, the joint-detected received signal is demultiplexed into a desired signal (ie, symbol or chip) and the interference signal, and then the interference signal is discarded.

  In some embodiments of the present invention, the acquisition / tracking and channel estimation signal processing operations may be explicitly performed individually, and in other embodiments of the present invention, the acquisition / tracking signal processing operations may be performed by channel estimation. It is envisioned that it may be performed as part of the operation.

  In certain embodiments of the present invention, as will be appreciated by those skilled in the art, if a finite signature sequence is used, the signal acquisition and / or tracking and channel estimation procedures for interference signals may be performed exhaustively. Good. This is especially the case when prior knowledge of the nature of the interference signal is not available. In such an embodiment, the signature sequence is not limited to, for example, a synchronization sequence and a channel estimation sequence, and may be received as a general term including the signature sequence.

  Alternatively, in certain embodiments of the present invention, information may be available about the nature of the interference signal that can be expected. In such alternative embodiments, a fairly small set of signature sequences may be searched to determine the presence or absence of an interfering signal.

  Because of the approximation that is performed (eg, a time shift in the channel estimation of the interference signal that leads to an approximate synchronization signal assumption), the interference signal output from the detector (ie, symbol, chip, etc.) may be erroneous. Should be noted. In particular, these outputs may be time shifted, phase rotated / distorted, or non-orthogonal (as a result of discarding the absolute time information of the interference signal). For example, they may still be considered to interfere with each other. A notable advantage of this operation is that the presence of such interference signals is considered during detection of the desired signal compared to current systems where only synchronous interference signals are considered. In that point. Thus, embodiments of the present invention allow superior performance from the detector, ie, reduce or partially reduce asynchronous interference signals.

  As mentioned above, the approximation performed in the detection method can result in corruption of the output of the detected interference signal. Thus, in one embodiment of the present invention, it is envisaged that a detection method that can handle corruption of the output of the detected interference signal is used. In this regard, it is envisaged that the detection method may not make an explicit assumption about the phase or energy of the detected interference signal. Suitable detection method candidates may include linear MUD types such as an inverse correlation receiver or a minimum mean square error (MMSE) linear detector.

  It should be noted that one or more additional degrees of freedom may need to be provided in order to mitigate the interference signal with a linear detector. That is, the more signals that are detected, the greater the degree of freedom required to utilize this information using a linear detector for the detection process. This may be achieved by utilizing some feature of the signal, such as spreading the band in a system incorporating some aspect of CDMA and / or multiple antennas to utilize the spatial domain.

  For clarity, it will be appreciated that the embodiments of the invention described above may be used with different functional units or processors. However, it will be appreciated that any suitable distribution of functionality among different functional units or processors may be used without departing from the invention, for example with respect to the detector. For example, functionality illustrated as being performed by separate processors or controllers may be performed by the same processor or controller. Accordingly, references to specific functional units should not be construed as strict logical or physical structures or configurations, but only as references to appropriate means of providing the described functions.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The present invention may optionally be implemented at least in part as computer software running on one or more data processors and / or digital signal processors. Accordingly, the elements and components of an embodiment of the invention may be implemented in any suitable manner physically, functionally and logically. Indeed, the functions may be implemented as part of a single unit, multiple units or other functional units. The foregoing methods and apparatus for mitigating asynchronous interference in cellular communication systems are envisioned to provide one or more of the following advantages.
(i) provide an accurate estimate of the received signal in a communication system in which there is an interfering (and substantially asynchronous) signal;
(ii) The concept of the present invention can be applied to a TD-CDMA system or an OFDM system.
(iii) The communication link can be operated with a high signal-to-noise ratio (SNR) and can therefore provide a corresponding increase in data throughput.
(iv) The communication link can operate when there is a significant level of interference (eg from other simultaneous links). In this case, the two (or more) communication links are considered time asynchronous.

  Although the present invention has been described with respect to particular embodiments and exemplary drawings, those skilled in the art will recognize that the invention is not limited to the described embodiments or drawings. While some embodiments of the present invention have been described using UMTS technology in some cases, those skilled in the art will recognize that such terms are also used in a general sense and that the present invention is not limited to such systems. recognize.

  Those skilled in the art will recognize that the operations of the various embodiments may be implemented using hardware, software, firmware, or combinations thereof, as appropriate. For example, certain processes may be performed with software, firmware or wiring logic modules, using a processor or other digital circuitry (the term “logic module” herein is used to perform the described functions). A fixed hardware, programmable logic module and / or suitable combination thereof, as will be appreciated by those skilled in the art). Software and firmware may be stored on computer-readable media. Other processes may be implemented using analog circuitry, as is well known to those skilled in the art. Further, memory or other storage devices may be used in embodiments of the present invention, as well as communication components.

  FIG. 6 illustrates an exemplary computer system 600 that may be used to perform the processing functions of an embodiment of the present invention. For example, this type of computer system may be used in Node B (especially Node B scheduler), core network elements (such as GGSN and RNC). Those skilled in the art will also recognize how to implement the invention using other computer systems or architectures. For example, the computer system 600 may be a desktop, laptop or notebook computer, handheld computing device (PDA, mobile phone, palmtop, etc.), mainframe, supermarket, so that it may be desirable or appropriate for a given application or environment. A computer, server, client, or other type of dedicated or general purpose computer device may be represented. Computer system 600 may include one or more processors (such as processor 604). The processor 604 may be implemented using a general purpose or special purpose processing engine (eg, a microprocessor, controller, or other control logic module, etc.). In this example, processor 604 is connected to a bus 602 or other communication medium.

  Computer system 600 may also include main memory 608 (such as random access memory (RAM) or other dynamic memory) that stores instructions and information for execution by processor 604. Main memory 608 may also be used to store temporary variables or other intermediate information during execution of instructions executed by processor 604. Computer system 600 may also include a read only memory (ROM) or other static storage device coupled to bus 602 for storing processor 604 instructions and static information.

  Computer system 600 may also include an information storage system 610. For example, the information storage system 610 may include a media drive 612 and a removable storage interface 620. Media drive 612 supports fixed or removable storage media (hard disk drive, floppy disk drive, magnetic tape drive, optical disk drive, CD or DVD drive (R or RW) or other removable or fixed media drive). A drive or other mechanism may be included. For example, storage medium 618 may include a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read and written by media drive 614. As these examples illustrate, the storage media 618 may include computer readable storage media that stores particular computer software or data.

  In alternative embodiments, information storage system 610 may include other similar components that allow a computer program or other instructions or data to be loaded into computer system 600. For example, such components may include a removable storage unit 622 and an interface 620 (such as a program cartridge and cartridge interface) that allow software and data to be transferred from the removable storage unit 618 to the computer system 600, and a removable Removable memory (eg, flash memory or other removable memory module) and memory slots, and other removable storage units 622 and interfaces 620 may be included.

  Computer system 600 may also include a communication interface 624. Communication interface 624 may be used to allow software and data to be transferred between computer system 600 and external devices. Examples of the communication interface 624 may include a modem, a network interface (such as an Ethernet or other NIC card), a communication port (such as a USB port), a PCMCIA slot, a card, and the like. Software and data transferred via communication interface 624 are in the form of signals that may be electronic, electromagnetic, optical, or other signals receivable by communication interface 624. These signals are provided to communication interface 624 via channel 628. This channel 628 may carry signals and may be implemented using wireless media, wired or cable, optical fiber, or other communication media. Some examples of channels include telephone lines, cellular telephone lines, RF lines, network interfaces, local area networks or wide area networks, and other communication channels.

  In this document, the terms “computer program product”, “computer readable medium”, etc. may be commonly used to refer to media (eg, memory 608, storage device 618, storage unit 622, etc.). These and other forms of computer readable media may store one or more instructions used by processor 604 to cause the processor to perform a specified operation. When such instructions (generally referred to as “computer program code”) (computer program code may be grouped into a computer program form and may be grouped into other groups) are executed In addition, it enables computer system 600 to perform the functions or functions of the embodiments of the present invention. The code may cause the processor to perform specified operations directly, may be compiled and executed, and / or other software, hardware and / or firmware elements (eg, libraries that perform standard functions) Note that it may be executed in combination with).

  In embodiments where the elements are implemented using software, the software may be stored on a computer-readable medium and loaded into computer system 600 using, for example, removable storage drive 614, drive 612, or communication interface 624. Good. The control logic module (in this example, software instructions or computer program code), when executed by the processor 604, causes the processor 604 to perform the functions of the present invention described herein.

  For clarity, it can be seen that the foregoing description has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processors or domains may be used without departing from the invention. For example, functionality illustrated to be performed by another processor or controller may be performed by the same processor or controller. Thus, a reference to a particular functional unit is not to indicate a strict logical or physical structure or configuration, but is only regarded as a reference to a suitable means for providing the desired function.

  Although the invention has been described with reference to several embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the claims. Further, although features may appear to be described with respect to particular embodiments, those skilled in the art will appreciate that the various features of the foregoing embodiments may be combined in accordance with the present invention.

  Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by eg a single unit or processor. Further, although individual features may be included in different claims, they may be advantageously combined in some cases, so that different claims do not make a combination of features feasible and / or advantageous It does not mean that it is not. Also, the inclusion of a feature in one category of claims does not indicate a limitation to this category, but this feature may be applicable to other claim categories as well, if necessary. Indicates.

  Although the invention has been described with reference to several embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the claims. Further, although features may appear to be described with respect to particular embodiments, those skilled in the art will appreciate that the various features of the foregoing embodiments may be combined in accordance with the present invention. In the claims, the term 'comprising' does not exclude the presence of other elements or steps.

  Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by eg a single unit or processor. Further, although individual features may be included in different claims, they may be advantageously combined in some cases, so that different claims do not make a combination of features feasible and / or advantageous It does not mean that it is not. Also, the inclusion of a feature in one category of claims does not indicate a limitation to this category, but this feature may be applicable to other claim categories as well, if necessary. Indicates.

  Further, the order of the features in the claims does not indicate any particular order in which the features must be performed; in particular, the order of the individual steps in a method claim must be performed in that order. It does not indicate what must be done. Rather, the steps may be performed in any suitable order. Further, the singular does not exclude a plurality. Accordingly, references to 'one', 'first', 'second', etc. do not exclude a plurality.

Claims (15)

A communication unit having a receiver for receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal,
The receiver includes a detection logic module configured to detect and process the composite communication signal as if the at least one asynchronously received interference signal was received in synchronization with the desired signal. communication unit. A synchronization logic module operably coupled to the detection logic module;
The composite communication signal of claim 1, wherein the composite communication signal is input to a synchronization logic module that synchronizes the timing of the communication unit with respect to both the desired signal and the at least one asynchronously received interference signal. communication unit. A channel estimation logic module operably coupled to the detection logic module;
The communication unit according to claim 1 or 2, wherein the desired signal and the at least one asynchronously received interference signal are applied independently to each channel estimation logic module.   The communication unit according to any one of claims 1 to 3, wherein the detection logic module discards the at least one asynchronously received interference signal following execution of a detection operation.   The detection logic module is configured to ignore at least one of a timing of the at least one asynchronously received interference signal and a phase shift of the at least one asynchronously received interference signal; The communication unit according to any one of claims 1 to 4.   6. The communication unit of claim 5, wherein the detection logic module processes the at least one asynchronously received interference signal within a processing window of the received desired signal in response to the ignoring operation.   The communication according to any one of claims 1 to 6, wherein the detection logic module comprises at least one of a joint detector, a linear detector, a multi-signal detector, and a multi-user detector. unit.   The communication unit according to any one of claims 1 to 7, wherein the composite communication signal comprises at least one burst of time slot communication signals.   The communication unit according to claim 8, wherein the time slot signal is at least one from a group of a time division code division multiplexing (TD-CDMA) access communication signal and an orthogonal frequency division multiplexing (OFDM) communication signal.   The communication unit according to any one of claims 1 to 9, wherein the communication unit is configured to support 3GPP cellular communication.   The communication unit according to any one of claims 1 to 10, wherein the communication unit is one from a group of a radio base station and a radio subscriber communication unit. A method for reducing interference in a communication system, comprising:
Receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal;
Detecting and processing the composite communication signal as if the at least one asynchronously received interference signal was received synchronously with the desired signal. A logic module for receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal;
An integrated circuit comprising: a detection logic module configured to detect and process the composite communication signal as if the at least one asynchronously received interference signal was received synchronously with the desired signal. A computer program product having program code for reducing interference in a cellular communication system, comprising:
Receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal, and as if the at least one asynchronously received interference signal was received synchronously with the desired signal; A computer program product having program code for detecting and processing the composite communication signal. A communication system having a communication unit capable of receiving a composite communication signal having a desired signal and at least one asynchronously received interference signal,
A communication system having a detection logic module that detects and processes the composite communication signal as if the at least one asynchronously received interference signal was received in synchronization with the desired signal.

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